DESCRIPTION: This is a application proposes experiments designed to prepare and characterize a stable, non-toxic andefficacious liposomal bupivacaine formulation that can be used in the clinical setting. The principal investigator, has proposed fourspecific aims.The first aim is to prepare various dehydrated-rehydratedliposomalvesicle formulations and to characterize these vesicles with respectto concentration of entrapped drug and in vitro release kinetics. The investigator will prepare a number of different dehydrated-rehydrated vesicles by altering the concentration of two saturated matrix lipids, the concentration of bupivacaine in the hydrating solution and the pH at which hydration occurs. The eight formulations with the highest drug/phospholipid ratios will then be used to measure the release of the entrapped drug over time. The second aim will be to evaluate the sterility, apyrogenicity and stability of these eight bupivacaine preparations. The liposomal bupivacaine formulations will be prepared under aseptic conditions and the sterility of each formulation will be tested by culturing under aerobic and anaerobic conditions. Apyrogenicity will be evaluated by injecting known aliquots IV in rabbits and monitoring body temperature. Formulations found to be sterile and apyrogenic will be stored at 4 degrees Celsius and assessed for physical and chemical stability at 3 month intervals. The third aim will be to determine the local and systemic toxicity of the liposomal bupivacaine preparations using in vivo and in vitro techniques. Metabolic perturbations of cartilage will be assessed by incubating bupivacaine preparations with bovine articular cartilage in the presence of radiolabeled sulfate and measuring sulfate incorporation as an indicator of proteoglycan synthesis. The in vivo local toxicity will be evaluated by injecting the formulations into the sciatic nerve in rats and the articular cartilage of rabbits and examining the tissue using light and electron microscopy. Systemic toxicity will be evaluated by injecting the liposomal bupivacaine preparations IP into mice and measuring LD50. Systemic organ toxicity will be determined by examining the liver, spleen, kidneys and lungs for pathologic changes. Finally, the fourth aim will be to evaluate the efficacy of the liposomal preparations. The formulations exhibiting optimal stability and lack of toxicity will be tested for efficacy and duration of analgesia using the mouse tail-flick test. The four formulations exhibiting the most prolonged analgesia will be further tested in a rabbit tooth pulp model.